Viewstate is the part of an ASP.Net page that stores the state of the page so that when a round-trip is made to the server (like when a button is pressed) the value of the various form fields or data grids isn't lost. In many cases viewstate isn't needed because the data can readily be reloaded from the server at less 'cost' to both the server and the client. However, ASPDNSF doesn't pay close attention to viewstate, leaving it on (the default) when it can easily be turned off with no detriment to the page. There are lots of articles about how to understand and use viewstate; I'm sure Vortex will eventually get to cleaning up the code in that way.
As for now, I would suggest that you ignore the viewstate as you don't want to be changing a whole bunch of ASPDNSF code just to save a few KB here and there and make future upgrades more difficult.
ML9.3.1.1
SQL 2012 Express
VS 2010
Azure VM